1. Field of the Invention
The present invention relates to a brake system for a motorcycle, and particularly to a brake system for a motorcycle which causes wheel braking mechanism of the front wheel and wheel braking mechanism of the rear wheel to move in response to each other by use of an appropriate output ratio depending on driving conditions and a braking operation of the motorcycle.
2. Description of the Background Art
A brake system employing what is called a by-wire method (hereinafter referred to as a “by-wire method”) is known in the art. According to this type of brake system, an amount of operation of a braking operation unit, such as a hand lever or foot pedal, is detected electrically. Based on the detected value, the wheel braking mechanism, such as a wheel caliper, is operated by hydraulic pressure which has been generated by a hydraulic pressure modulator. An example of this type of brake system is described in Japanese Patent Laid-open Official Gazette No. Hei. 5-39008. The brake system disclosed in Japanese Patent Laid-open Official Gazette No. Hei. 5-39008 has the following schematic configuration.
Specifically, with regard to this type of brake system, a hydraulic pressure modulator which generates hydraulic pressure by use of an electric pump (electrically-operated actuator), a reservoir, a control valve and the like are merged and connected with a main brake line connecting wheel cylinders (wheel braking mechanism) of the respective wheels and a master cylinder which moves in response to a brake pedal (braking operation unit). In addition, a normally-open-type electromagnetic on-off valve is provided in a position in the main brake line. The position of the electromagnetic on-off valve is located toward the master cylinder from a portion in which the main brake line and the hydraulic pressure modulator are connected with each other. The electromagnetic on-off valve is a fail safe device. The electromagnetic on-off valve is energized, and blocks the path between the electromagnetic valve and the master cylinder, while a regular braking operation is performed. In addition, hydraulic pressure is generated by the hydraulic pressure modulator. The hydraulic pressure is generated corresponding to a detection value which has been found by electrically detecting an amount of operation of the brake pedal, and to other driving conditions of the vehicle.
Furthermore, this type of brake system can be provided with a hydraulic pressure modulator corresponding to the wheel cylinder of each wheel, thereby enabling hydraulic pressure and the like supplied to each wheel cylinder to be adjusted in an arbitrary manner.
However, in the conventional brake system, while a regular braking operation is performed except for fail safe, the master cylinder is designed to be cut off from the main brake line by an ON operation of the electromagnetic on-off valve. Concurrently, all of the wheel braking mechanism are designed to be operated by use of hydraulic pressure which has been generated by the hydraulic pressure modulator. For this reason, electric current is constantly consumed while the braking operation is performed due to is use in the ON operation of the electromagnetic on-off valve and to its use in the operation of all hydraulic pressure modulators.
For this reason, if the electromagnetic brake as described above were employed in a motorcycle brake system, the battery and the generator would need to be constructed in a larger size. This is an undesireable situation for the motorcycle which is required to be smaller in size and lighter in weight.
For motorcycles, a Combined Brake System, hereinafter referred to as a “CBS”, has been developed. This system causes the wheel braking mechanism of the front wheel and the wheel braking mechanism of the rear wheel to move in response to an operation of a brake operating unit of one of the circuits by use of an appropriate output ratio depending on driving conditions and a braking operation of the motorcycle. Thus, the wheel braking mechanism of the front wheel and the wheel braking mechanism of the rear wheel is operated, even when any single one of the front wheel brake and the rear wheel brake is operated.
In order to realize this system without complicating the wheel braking mechanism and piping, adoption of the aforementioned by-wire method has been brought to attention. Specifically, in the by-wire method, a front wheel brake circuit and a rear wheel brake circuit are completely independent of each other, thereby enabling the wheel braking mechanism of each of the two brake circuits to be controlled in an arbitrary manner while reflecting an amount of braking operation and driving conditions which have been electrically detected. For this reason, a piston exclusively for causing the two wheel braking mechanism to move in response to each other needs not be added to each of the two wheel braking mechanism. In addition, piping exclusively for causing the two wheel braking mechanism to move in response to each other needs not be added to each of the two wheel braking mechanism. Accordingly, with regard to this type of brake system, a problem to be solved is how electric current consumption can be reduced while advantages of the by-wire method are employed.
Furthermore, it has been considered that an anti-lock brake system (hereinafter referred to as an “ABS”) is fitted into brake systems for motorcycles in addition to the aforementioned CBS being fitted thereinto. A main task of the CBS is to actively supply hydraulic fluid to the main brake line depending on an input signal. By contrast, a main task of the ABS is to decrease, maintain, and again increase, hydraulic pressure in the main brake line depending on an input signal. For this reason, normally, a hydraulic pressure modulator exclusive for the CBS, and a separate hydraulic pressure modulator exclusive for the ABS are fitted into the brake system. If, however, the hydraulic pressure modulator exclusive for the CBS and the hydraulic pressure modulator exclusive for the ABS were to be fitted into the brake system for motorcycles, not only would the number of parts increase, but also bulkiness and extra weight would be introduced into the brake system. Accordingly, it is desirable that a single hydraulic pressure modulator is used as a component for performing a plurality of functions related to controlling hydraulic pressures.
With this taken into consideration, an object of the present invention is to realize a CBS without complicating the wheel braking mechanism and the piping, and without increasing the electric current consumption, and further to accordingly provide a brake system for a motorcycle which is smaller in size and lighter in weight.
In addition, another object of the present invention is to make a single hydraulic pressure modulator available as a component for performing a plurality of functions related to controlling hydraulic pressures without complicating the structure of the hydraulic pressure modulator, and to accordingly provide a brake system for a motorcycle which is smaller in size and lighter in weight.
In order to achieve the aforementioned objectives, according to a first aspect of the present invention, a front wheel brake circuit and a rear wheel brake circuit are provided independently of each other. Each of these brake circuits is configured to include: a master cylinder which moves in response to a braking operation unit of each wheel; wheel braking mechanism for applying braking force to a corresponding wheel by hydraulic pressure operation; a main brake line through which the master cylinder and the wheel braking mechanism are connected with each other; a hydraulic pressure modulator for causing an electrically-operated actuator to generate hydraulic pressure depending on driving conditions and a braking operation of the vehicle, and for supplying the hydraulic pressure to the main brake line and discharging the hydraulic pressure from the main brake line while the hydraulic pressure modulator is merged and connected with the main brake line; and an electromagnetic on-off valve which is provided in a position in the main brake line, the position being located toward the master cylinder from the portion where the main brake line and the hydraulic pressure modulator are merged and connected with each other. The electromagnetic on-off valve controls the communicative connection and cutoff between the master cylinder and the wheel braking mechanism.
In the brake system of a motorcycle, the electromagnetic on-off valve and the electrically-operated actuator of each of the two brake circuits are controlled depending on driving conditions and a braking operation of the vehicle, thereby causing the wheel braking mechanism of the two respective brake circuits to move in response to each other, and to be operated, by use of an arbitrary output ratio. In the brake system for a motorcycle, when the wheel braking mechanism of the two respective brake circuits are intended to be caused to move in response to each other and to be operated, the electromagnetic on-off valve is designed to be caused to open so that the wheel braking mechanism is operated by use of hydraulic pressure from the master cylinder, in a brake circuit connected to one braking operation unit which has been operated earlier than the other braking operation unit. In the other brake circuit, the electromagnetic on-off valve is designed to be caused to close so that the wheel braking mechanism is operated by use of hydraulic pressure from the hydraulic pressure modulator.
In a brake system that is configured in the aforementioned manner, hydraulic pressure generated by the master cylinder is supplied directly to wheel braking mechanism connected to a braking operation unit which has been operated earlier than the other braking operation unit. Furthermore, hydraulic pressure generated by the hydraulic pressure modulator is supplied to the other wheel braking mechanism by use of the by-wire method. Consequently, according to the CBS of this system, hydraulic pressure is generated by the electrically-operated actuator only in a brake circuit connected to a braking operation unit which has been operated later than the other braking operation unit. In addition, at this time, the electromagnetic on-off valve is energized only in one of the two brake circuits.
A brake system for a motorcycle according to a second aspect of the present invention has the same configuration as the brake system for a motorcycle according to the first aspect of the invention, except for the following addition. The hydraulic pressure modulator is configured to include a piston which receives force from the electrically-operated actuator, and which accordingly moves back and forth in a cylinder. The inside of the cylinder is divided into two areas by a position almost in the center of the cylinder. When the piston is positioned in this generally central position, it is considered to be in a neutral reference position. In use, the piston is to be caused to operate in one area and the other area of the two areas respectively. Different modes of control of the hydraulic pressure are characterized by operation of the piston in one area and operation of the piston in the other area, respectively.
In a brake system for a motorcycle configured in the aforementioned manner, the piston is controlled in the two operation areas separated by the neutral reference position, thereby enabling the single hydraulic pressure modulator to be used as a component for performing two separate functions of controlling hydraulic pressures.
A brake system according to a third aspect of the present invention has the same configuration as the brake system according to the second aspect of the present invention, except for the following addition. The piston separates and forms a hydraulic pressure chamber in the cylinder. An operation area of the piston where the hydraulic pressure chamber is expanded by displacement of the piston from the neutral reference position is designed to be used for the anti-lock brake control (ABS control). The other operation area of the piston is designed to be used for control for causing the wheel braking mechanism of the two respective brake circuits to move in response to each other (CBS control).
In a brake system configured in the aforementioned manner, according to the ABS control, control of hydraulic pressure such as decompression, maintenance and re-compression is performed by causing the piston to start operating from the neutral reference position in a direction which expands the volume of the hydraulic pressure chamber. Furthermore, according to the CBS control, hydraulic fluid is supplied to, and discharged from, the main brake line by causing the piston to start operating from the neutral reference position in a direction which reduces the volume of the hydraulic pressure chamber.
A brake system according to a fourth aspect of the present invention has the same configuration as the brake system according to the third aspect of the present invention, except for the following addition. The hydraulic pressure modulator includes energizing means for applying a force to the piston in a direction which reduces the volume of the hydraulic pressure chamber, and a stopper for controlling displacement of the piston by the energizing means at the neutral reference position. Thereby, if the electrically-operated actuator of the hydraulic pressure modulator is stopped from being energized while the ABS control is performed, the piston is designed to be returned to the neutral reference position by the energizing means and the stopper.
In a brake system configured in the aforementioned manner, the piston is returned to the neutral reference position by the energizing means and the stopper without an electric power supply when the electrically-operated actuator is stopped from being energized in the course of the ABS control.
A brake system according to a fifth aspect of the present invention has the same configuration as the brake system according to the fourth aspect of the present invention, except for the following addition. An electromagnetic on-off valve of normally-closed type is provided between the hydraulic pressure chamber and the main brake line. In addition, a bypass path which bypasses the electromagnetic on-off valve, and through which the hydraulic pressure chamber and the main brake line are connected to each other, is provided. Furthermore, the bypass path is provided with a check valve which allows hydraulic fluid to flow from the hydraulic pressure chamber to the main brake line.
In a brake system configured in the aforementioned manner, the electromagnetic on-off valve is closed while being stopped from being energizing, thereby blocking the flow of hydraulic fluid from the main brake line to the hydraulic pressure chamber. However, the flow of hydraulic fluid from the hydraulic pressure chamber to the main brake line is secured by the check valve and the bypass path. Accordingly, even if the energizing is stopped in the course of the ABS control, excess hydraulic fluid which remains in the hydraulic pressure chamber would be returned to the main brake line.
According to the first aspect of the present invention, hydraulic pressure which has been generated by the master cylinder is supplied to the wheel braking mechanism, in a brake circuit connecting to a braking operation unit which has been operated earlier than the other braking operation unit. In the other brake circuit connecting to a braking operation unit which has been operated later, hydraulic pressure which has been generated by the hydraulic pressure modulator is supplied to the wheel braking mechanism by the by-wire method. Thereby, electric current consumption by the electrically-operated actuator can be largely reduced in comparison with a case where hydraulic pressure which has been generated by the hydraulic pressure modulator is supplied to both brake circuits. In addition, an electromagnetic on-off valve in only one of the two brake circuits may be energized while the CBS control is performed. Accordingly, electric current consumption by the electromagnetic on-off valve can be also reduced. Consequently, the present invention enables the CBS to be realized without complicating the wheel braking mechanism and piping, and without introducing bulkiness and extra weight associated with a larger battery and generator.
In addition, according to the second aspect of the present invention, the piston is controlled in the two operation areas which are separated by the neutral reference position. Thus, the single hydraulic pressure modulator is used as a component for performing two separate functions of controlling hydraulic pressures. Accordingly, the whole of the system is smaller in size and lighter in weight, which is advantageous for a system being mounted onto a motorcycle.
According to the third aspect of the present invention, the control of hydraulic pressure for the ABS and the control of hydraulic pressure for the CBS are realized by the single hydraulic pressure modulator without causing trouble.
According to the fourth aspect of the present invention, even if the electrically-operated actuator is stopped from being energized while the ABS control is performed, the piston is returned to the neutral reference position. Accordingly, the piston can be ready for the next control of the ABS and the CBS.
According to the fifth aspect of the present invention, even if the energizing is stopped while the ABS control is performed, hydraulic fluid in the hydraulic pressure chamber can be returned to the main brake line. Accordingly, the fail safe to be performed while the ABS control is performed can be realized with a simple structure.
Modes for carrying out the present invention are explained below by reference to an embodiment of the present invention shown in the attached drawings. The above-mentioned object, other objects, characteristics and advantages of the present invention will become apparent form the detailed description of the embodiment of the invention presented below in conjunction with the attached drawings.